Jul 14, 2004

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Transgenic fructane potatoes: phenotypical characteristics and susceptiblity to major pests and diseases

(2001 – 2004) Federal Biological Research Centre for Agriculture and Forestry (BBA), Institute for Integrated Plant Protection, Kleinmachnow

Topic

Fructan potatoes have a modified carbohydrate metabolism. They produce inulin, a sugar which is novel to potato, and have an increased total soluble sugar content.

Altering the potato’s carbohydrate metabolism, especially increasing levels of soluble sugars, could change potentially change the potato’s nutritional value for pathogens. Phytopathological changes are therefore considered possible.

To address this question, the transgenic fructan potato was compared with a conventional counterpart and with five other conventional varieties to check for differences in susceptibility to potato late blight, potato wart, nematodes and the Colorado potato beetle. The field trials were carried out with six different transgenic lines.

Summary

There were no changes in yield compared with the conventional variety Désirée. The starch content, however, was reduced, while the fructan (inulin) content increased (approx. 2%). The transgenic potatoes possess a shorter main stem and do not form a closed canopy. This means they are subject to more competition from weeds and makes the microclimate more conducive to foliar diseases. Any observed variations in susceptibility of transgenic potatoes to pests and diseases (late blight, potato wart, nematodes, and the Colorado potato beetle) were not statistically significant and did not exceed the natural variation that exists for conventional potatoes. Fructan potatoes are not expected to behave differently from conventional potato varieties with respect to cultivation and pathology.

Experiment description

To record possible phenotypic variations in transgenic potato varieties development data were collected regularly, along with digitalised images of the development of the potato and data on yield, weather and the occurrence of pests. The field research was complimented by work in the laboratory and in greenhouses.

The study investigated the following questions:

• Does this genetic modification affect the potato’s phenotype, especially the characteristics that are important for yield such as tuber weight and size?
• Are transgenic potato varieties more susceptible to pests than conventional potatoes?
• Does the increased level of soluble sugars in fructan potatoes enhance the effectiveness of Bacillus thuringensis (Bt) against the Colorado potato beetle?
• Does the altered carbohydrate metabolism result in enhanced cold tolerance that could make it more likely for tubers to survive winters in fields? Overwintering tubers are undesired as they present the danger of acting as a reservoir for phytopathogenic viruses.

Results

In 2001, 2002 and 2003, six transgenic potato varieties and their conventional counterpart varieties were grown on the BBA’s field test site (about 400 plants per variety). In 2002, militant anti-GMO activists almost completely destroyed the site only six weeks after planting. Although field tests were not possible for that growing season, tests were carried out in the lab and in greenhouses. In cooperation with the Federal Agricultural Research Centre (FAL), the first feeding studies on pigs were carried out in 2004 using the 2003 crop.

Growth form. After three years of cultivation it was determined that the transgenic lines transformed with the construct SST/FFT (fructan potato) had a modified growth form compared with potatoes transformed with the SST construct and with the conventional parental variety Désirée. All other external characteristics of the transgenic lines corresponded with their conventional counterparts.

Yield and starch level. In 2001 and 2003, the yield from the transgenic lines was equal to that of their conventional counterparts. High starch content was retained in the transgenic lines, compared with their conventional counterparts, although the SST/FFT transgenics had slightly lower levels to compensate for the presence of fructan.

Susceptibility to diseases in the field. After three years of field trials there were no indications that the transgenic lines had any differences in susceptibility to diseases from their conventional counterparts. Therefore, changes in pesticide use from cultivating fructan potatoes is not expected.

Laboratory. Under standardised laboratory conditions, it was observed that the transgenic fructan potato tubers (only the tubers) were less susceptible to late blight than the conventional varieties. It is suspected that the effected changes in carbohydrate composition could affect the development of the pathogen. Any implications this could have on disease management are still being evaluated. No differences were observed between transgenic and conventional potato leaves to late blight infection. Other pests and diseases, including the Colorado potato beetle and nematodes, did not seem to be affected by the genetic modification of their host plants.

Volunteers. No transgenic potato volunteers were found as a result of an increase in coldtolerance.